If I2C wasn’t enabled during the pimoroni-dashboard setup of the phat, I’d have done it via sudo raspi-config (and rebooted).

I was trying this on a USB-stem pi zero but am going to try again tonight with a “proper” Pi (will rule out the GPIO headers but they are fine with other pHATs). I’ll also do a fresh stretch lite install and start again from scratch.

As an added bonus, the hyper pixel changes also prevented me asking similar questions about the BM680 breakout board not working. I’d convinced myself I’d damaged it by plugging it in the wrong way round ;-) Nope! It’s fine (once the hyper pixel lines were commented out of the config.txt).